Manufacture of copper oxide

ABSTRACT

A method for the production of copper oxide or zinc hydroxide which comprises contacting metallic copper or zinc is contacted with an aqueous solution containing oxygen or an oxygencontaining gas, ammonia and an ammonium salt which is preferably ammonium nitrate. The concentration of ammonia is maintained above 4 moles per mole of dissolved copper and the aqueous solution of copper ammine or zinc ammine is separated from any undissolved metal before it becomes saturated with the metal and then heated to precipitate copper oxide or zinc hydroxide from the solution. Preferably the heating is carried out in the absence of added alkali and in the presence of a stream of purging gas and the mother liquor and the purging gas are recycled.

United States Patent [1 1 Joice et al.

[ 1 Sept. 18, 1973.

[ MANUFACTURE OF COPPER OXIDE [22] Filed: Sept. 23, 1971 21 Appl. No.: 183,274

[52] US. Cl. 423/604, 423/622 [51] Int. Cl C0lg 3/02, COlg 9/02 [58] Field of Search 23/147; 75/82, 117,

[56] 7 References Cited UNITED STATES PATENTS 3/1972 Burke 23/147 11/1926 Edwards et al. 75/l17 Primary Examiner-Oscar R. Vertiz Assistant Examiner-Hoke-S. Miller Attorney-Herbert H. Goodman [57] ABSTRACT A method for the production of copper oxide or zinc hydroxide which comprises contacting metallic copper or zinc is contacted with an aqueous solution containing oxygen or an oxygen-containing gas, ammonia and an ammonium salt which is preferably ammonium nitrate. The concentration of ammonia is maintained above 4 moles per mole of dissolved copper and the aqueous solution of copper ammine or zinc ammine is separated from any undissolved metal before it becomes saturated with the metal and then heated to precipitate copper oxide or zinc hydroxide from the solu tion. Preferably the heating is carried out in the absence of added alkali and in the presence of a stream of purging gas and the mother liquor and the purging gas are recycled.

9 Claims, No Drawings MANUFACTURE OF COPPER OXIDE The present invention provides a method for the manufacture of copper oxide. The invention thus provides a valuable step in the manufacture of copper salts, such as copper dichromate. The invention is also applicable to the manufacture of zinc hydroxide.

The invention will be described hereinafter with particular reference to copper, but it will be understood that metallic copper may be replaced by metallic zinc or by alloys of copper and zinc without departing from the dichromate to chromate The long-lasting effectiveness of wood preservative compositions containing sodium dichromate and a copper salt, such as copper sulphate, is considered to be due to the fixation of the fungitoxic copper within the wood, probable as copper chromate, formed after the conversion of dichromate to chromate by the wood substance. This process is, however, accompanied by the formation of inert sodium salts, which dilute the active ingredients and adversely affect the adhesion of paint, if subsequent crystallisation of such salts occurs at the wood surface.

We considered the posssibility of improving wood preservatives by incorporating therein a preformed copper dichromate. However the known methods of preparing copper dichromate proved uneconomic. For example, the reaction of solutions of copper sulphate and sodium dichromate led to the formation of a double salt, with resulting wastage of copper, reaction of metallic copper with chromic acid under a variety of conditions, all led to the reduction of an uneconomically large amount of hexavalent chromium to trivalent chromium. Attempts to dissolve coppper in nitric acid, add chromic acid to the solution and distill off nitric acid, also proved difficult on a technical scale and we were therefore compelled to consider the reaction of copper oxide with chromic acid. This latter method appeared unattractive because of the high cost and/or low rate of dissolution of commercially available copper oxide, and because none of the published methods for preparing copper oxide promised any better prospects.

We have now discovered an economical method for the manufacture of an acid soluble copper oxide which is suitable for use in the manufacture of copper dichromate, and also of a wide range of copper salts which present problems similar to any of those described above in relation to the dichromate.

Hitherto commercial copperoxide has been prepared by heating copper in air, or by heating copper nitrate. Neither of these methods produces a product which is satisfactory as a source of cupric salts. It is known that copper oxide can be precipitated from solutions of copper ammine by addition of alkali thereto. Known methods of preparing ions of copper ammines by dissolving metallic copper in aqueous ammonia, are, however, undesirably slow and inefficient.

We have now devised a method for the rapid and efficient production of cuprammonium salts. We have further discovered that the copper ammines may be decomposed by heating in solution so as to recover the copper as an acid soluble oxide and the other staring materials in a form suitable for reuse in the preparation of further copper ammines. Copper oxide produced according to the invention is a convenient source for the manufacture of cupric salts, including copper dichromate.

Our invention provides a method for the manufacture of copper oxide and/or zinc hydroxide which comprises contacting metallic copper and/or zinc with oxygen and an aqueous solution of ammonia and an ammonium salt, sufficient to dissolve the metal as a metal ammine, separating the solution of metal ammine from any undissolved metal and heating the metal ammine to precipitate copper oxide and/or zinc hydroxide.

The metallic copper may be granular, wire, scrap, copper rings or any other convenient physical form. Since the reaction occurs at the suface of the copper, an adequate surface area must be exposed to the reaction mixture, but it is not necessary for the copper to be very finely divided. Satisfactory reaction has been achieved in a column packed with copper rings.

We have found that good contact between oxygen and the copper surface is of great importance in achieving a high rate of reaction. The oxygen may conveniently be bubbled through the reaction mixture in such a manner that adequate contact with the copper is achieved, by ensuring the presence of air spaces in the mass of copper. For example oxygen may be passed into a column containing the copper and reaction solution, through suitable distribution means (e.g. a sintered glass, or other finely perforated, plate) located in the base of the column, or else through a simple inlet. The oxygen may be used as the pure gas, or diluted with inert gases. Conveniently air, or air enriched with oxygen may be used as the source of oxygen.

The pressure in the reaction vessel is not critical. We have found it convenient to dissolve the copper at atmospheric pressure, but other pressures, e.g., superatmospheric pressures could be employed.

The temperature of the reaction mixture may be varied within wide limits. The reaction is operable at any temperature at which the reaction mixture is liquid, e.g., 10 to C. Preferably the initial temperature is between 15C and 45C, e.g., from 20C to 30C. It the reaction is allowed to proceed without any cooling the temperature will rise, e.g., from 25C initial temperature to 55C final temperature. If the reaction mixture is cooled the preferred steady temperature may be between 30C and 50C.

The concentration of ammonia must be sufficient to dissolve metallic copper, e.g., from 0.5 percent by weight up to saturation. The higher the ammonia concentration the more rapid the dissolution of copper, but the greater the loss of ammonia from the solution. Preferably the concentration of ammonia in the reaction solution is from 5 percent to 20 percent by weight. Preferably the ammonia concentration is maintained throughout at a value greater than 4 moles per mole dissolved copper.

The ammonium salt may preferably be ammonium chloride, ammonium sulphate, ammonium nitrate, ammonium carbonate or mixtures of ammonium salts. Most other water soluble ammonium salts are also effective, although the chromate and dichromate are not recommended. We have discovered that the use of ammonium nitrateis particularly advantageous, in that it does not tend to form basic copper nitrate when the solution is heated to precipitate copper oxide. Thus although the ammonium salt may generally be present in concentrations of from 0.5 percent to saturation, it is preferred, in the case of ammonium salts other than the nitrate to employ concentrations less then 5 percent and preferably less than 2.5 percent by weight or about 0.2 molar in the reaction solution, in order to avoid formation of basic copper salts. Ammonium nitrate, on the other hand may conveniently be employed in concentrations up to, for example, 16 percent by weight, with gains in the rate of dissolution of the copper but without formation of basic copper nitrate.

In general the rate of dissolution is proportional to the concentration of ammonium salt.

The rate of flow of oxygen or oxygen-containing gas through the system influences the rate of reaction and the rate of loss of ammonia. The greater the oxygen flow the greater the rate of dissolution of copper. it is therefore advantageous from the point of view of rate of reaction to have as high a concentration of oxygen in the gas as is feasible. Preferably the total amount of oxygen passed through the system while the reaction solution is in contact with the metallic copper is at least sufficient to provide approximately the stoichiometric quantity based on the equation:

Cu (NH X is a copper ammine, as defined in Chemical Elements and their Compounds by Sidgwick, Vol. 1, pages 156-157 (Oxford University Press 1950); with the corresponding zinc ammines being defined at pages 279-280. These are sometimes (and less preferably) referred to as coprammonium and zinc ammonium salts.

The dissolution of copper in the aqueous ammoniacal solution may be performed as a batch or a continuous or semi-continuous operation. In either case operation involves contacting copper with an aqueous solution of ammonia salt preferably containing an excess of ammonia based on the above stoichiometry. The initial concentration of dissolved copper is preferably zero and in any case less than saturation andthe solution is preferably separated from the metallic copper before the concentration of dissolved copper reaches saturation, so as to avoid precipitation of copper hydroxide on the surface of the metallic copper.

In the second stage of the method of our invention the solution of copper ammine is heated, e.g., to a temperature above 80C and preferably to boiling point. A purging gas, e.g., air, is preferably passed through the heated solution to assist in removing ammonia, according to the equation:

It is possible to add alkali at this stage, however, it is greatly preferred not to add any substantial amount of alkali and preferably to add no alkali at all, since the alkali reacts for example according to the equation:

which prevents the ammonium salt being recovered and leads to the formation of a relatively worthless sodium salt as by-product. On the other hand, in the absence of alkali, the ammonia and ammonium salt may each be recovered substantially quantitatively and reused. If air or other oxygen containing gas is used to purge the solution of ammonia, it may be directly recycled to the vessel in which the metallic copper is dissolved, and used to supply both oxygen and ammonia. The copper oxide settles out as a granular precipitate which is easily filtered to leave a clear aqueous solution of the ammonium salt ready to be reused directly in the dissolution of fresh metallic copper.

The copper oxide may be used as such or may be dissolved in a variety of acids to form cupric salts which can otherwise be prepared commercially only by a longer or more expensive sequence of steps. For example the copper oxide may be dissolved in chromic acid to form copper dichromate, or hydrochloric, formic, acetic or napthenic acids.

The invention is illustrated by the following example of which examples 1 and 4 to 8 are examples of the invention and examples 2 and 3 are comparative:

Example 1 A glass column, packed with gm. of copper rings, was filled with 200 ml. of a solution containing 11.2 gm. of NH;, and 20 gm. of ammonium nitrate. Air was passed into the base of the column at the rate of 250 ml.per minute, for 1 hour, and the temperature of the solution rose steadily from 25C to a maxiumum of 50C, 12.5 gm of copper were found to have dissolved at the completion of the reaction. The deep blue solution was then poured into a separate vessel, and steam and air were passed through the solution for 30 minutes. Ammonia was driven off and copper oxide was quantitatively formed as a heavy black precipitate. The clear ammonium nitrate solution was decanted, and recovered for further use.

Example 2 The procedure of example 1 was repeated in the absence of ammonia in the initial reaction solution. Under these conditions, only 1 gm. of copper was dissolved after 1 hour.

Example 3 The procedure of example 1 was carried out in the absence of ammonium nitrate in the initial reaction solution. Only 2 gm. of copper dissolved after one hour.

Example 4 The procedure of example 1 was carried out using 100gm. of pieces of thin zinc sheet in place of the hollow copper rings. A temperature rise-from 22C to 52C was recorded and 9.6 gm. of zinc were found to have dissolved after one hour. Air and steam were then passed through the clear colourless solution and zinc hydroxide was formed as a heavy white precipitate.

Example 5 The procedure of example 1 was followed using 100 gmfof hollow brass rings in place of the copper rings. 14.0 gm of the brass had dissolved after one hour.

Example 6 8 gm. of copper oxide, obtained according to example l, were added to 100 ml. of a cold solution of chromic acid containing 20 gm. of CrO The entire sample dissolved rapidly to yield a clear solution of copper dichromate.

In contrast, when 8 gm. of a commercial sample of copper oxide were added to a similar solution of chromic acid and the mixture heated for 2 hours, only 3.8 gm. were found to have dissolved.

Example 7 Example 8 A sample of copper oxide, obtained according to example 1, was added to an excess of naphthenic acid NA. 180 SP (supplied by Shell Chemicals Ltd.) dissolved in white spirit. The mixture was heated and stirred for two hours, after which the copper oxide was substantially dissolved to yield a deep blue/green solution of cupric naphthenate. Commercial grades of copper oxide were found to be almost completely unattacked by the acid under the above conditions.

We claim:

1. A method for the manufacture of a product selected from copper oxide and zinc hydroxide which consists in (a) contacting a metal M selected from copper, zinc and mixtures thereof with an oxygen containing gas and an aqueous solution consisting essentially of water, between 0.5 and 16 percent by weight of water soluble ammonium salt NH X, wherein X is the anion of said salt, and between 0.5 percent and saturation of ammonia, said ammonia being maintained at a concentration in said solution inan amount greater than 4 moles per mole of dissolved metal M, whereby metal M is dissolved to form the corresponding metal ammine M(NH ).,X

b. separating a solution of said metal ammine from any of said metal which may not have been dissolved;

c. heating the solution of said metal ammine at a temperature of at least 80C to precipitate the product therefrom; and

d. recovering the precipitated product.

2. The method according to claim 1 wherein the ammonium salt is ammonium nitrate in a concentration of from 5 to 16 percent by weight.

3. The method according to claim 1 wherein the ammonium is selected from ammonium chloride, ammonium sulphate and ammoniumcarbonate and is present in a concentration of less than 0.2 molar.

4. The method according to claim 2 wherein the temperature of the solution at the commencement of step 6 (a) is between 15C and 45C.

5. The method according to claim 5 wherein the solution is cooled during step (a) to maintain a steady state temperature between 30C and 50C.

6. The method according to claim 1 wherein the oxygen containing gas is selected from oxygen, air and mixtures thereof and is bubbled through a mixture of the metal and the aqueous solution.

7. The method according to claim 1 wherein an oxygen containing purging gas is passed through the solution during step (0), thereby stripping ammonia from the solution and forming a mixture ammonia with said purging gas and recycling said mixture to step (a) to provide at least part of the oxygen and ammonia required.

8. The method according to claim 1 wherein the aqueous solution is heated in the step (c) to boiling point, and the aqueous solution remaining after step (d) is recycled for use in step (a) 9. A method for the manufacture of copper oxide which comprises a. contacting metallic copper with an aqueous solution consisting essentially of water, from 5 to 16 percent by weight of ammonium nitrate and from 0.5 percent to saturation of ammonia;

b. passing an oxidising gas selected from oxygen, air and mixtures thereof through the solution while maintaining the concentration of ammonia in the solution at a value of at least 4 moles per mole of dissolved copper to form copper ammine, Cu(NH )NO in said solution;

c. before the said solution becomes saturated with copper, separating the solution from any copper which may not have been dissolved;

d. heating said solution at a temperature of from C to boiling, thereby forming a precipate of copper oxide;

e. passing a gas selected from oxygen, air and mixtures thereof through theheated solution, thereby forming a gaseous mixture of ammonia and said f. recycling said gaseous mixture from step (e) to provide at least part of the oxidising gas and the ammonia required at step (b);

g. separating the precipitated copper oxide from the aqueous solution remaining after step (c) and recovering said copper oxide as product; and

h. recycling said aqueous solution from step (g) to provide at'least part of the solution required in step 

2. The method according to claim 1 wherein the ammonium salt is ammonium nitrate in a concentration of from 5 to 16 percent by weight.
 3. The method according to claim 1 wherein the ammonium is selected from ammonium chloride, ammonium sulphate and ammonium carbonate and is present in a concentration of less than 0.2 molar.
 4. The method according to claim 2 wherein the temperature of the solution at the commencement of step (a) is between 15*C and 45*C.
 5. The method according to claim 5 wherein the solution is cooled during step (a) to maintain a steady state temperature between 30*C and 50*C.
 6. The method according to claim 1 wherein the oxygen containing gas is selected from oxygen, air and mixtures thereof and is bubbled through a mixture of the metal and the aqueous solution.
 7. The method according to claim 1 wherein an oxygen containing purging gas is passed through the solution during step (c), thereby stripping ammonia from the solution and forming a mixture ammonia with said purging gas and recycling said mixture to step (a) to provide at least part of the oxygen and ammonia required.
 8. The method according to claim 1 wherein the aqueous solution is heated in the step (c) to boiling point, and the aqueous solution remaining after step (d) is recycled for use in step (a)
 9. A method for the manufacture of copper oxide which comprises a. contacting metallic copper with an aqueous solution consisting essentially of water, from 5 to 16 percent by weight of ammonium nitrate and from 0.5 percent to saturation of ammonia; b. passing an oxidising gas selected from oxygen, air and mixtures thereof through the solution while maintaining the concentration of ammonia in the solution at a value of at least 4 moles per mole of dissolved copper to form copper ammine, Cu(NH3)NO2 in said solution; c. before the said solution becomes saturated with copper, separating the solution from any copper which may not have been dissolved; d. heating said solution at a temperature of from 80*C to boiling, thereby forming a precipate of copper oxide; e. passing a gas selected from oxygen, air and mixtures thereof through the heated solution, thereby forming a gaseous mixture of ammonia and said gas; f. recycling said gaseous mixture from step (e) to provide at least part of the oxidising gas and the ammonia required at step (b); g. separating the precipitated copper oxide from the aqueous solution remaining after step (c) and recovering said copper oxide as product; and h. recycling said aqueous solution from step (g) to provide at least part of the solution required in step (a). 